The present invention relates to a safety arrangement in a weapon, such as an automatic or semi-automatic small arm. The invention may find particular application in a rifle for firing caseless cartridges, having a bolt assembly which is movably mounted in the longitudinal direction of the rifle and movable relative to a barrel, further having an ammunition magazine, a cartridge feed mechanism and a trigger mechanism. The fully operational weapon system is contained in a dust and water-tight receiver designed as a stock.
A small arm of this type is disclosed in German Laid-Open Patent application (Offenlegungsschrift) No. 23 26 525.0. In this weapon, the entire, fully operation weapon system is shiftably mounted in a receiver designed as a stock. The slidability of the entire system provides accuracy advantages by eliminating or reducing recoil to a minimum during a limited number of shots or during a burst. This known small arm is also advantageous in that is satisifies more stringent demands, because the weapon system is located within the receiver and because the receiver is sealed against the external effects of dust and water. The only opening remaining is the muzzle. The receiver is only dust and water-tight, but not gas-tight.
It is a known fact that when a shot is fired, propellant gases are formed which contain combustible gas residues, in particular CO. When the bolt assembly is opened, there may still be considerable pressure in the barrel, which causes the residual gases to flow out at the chamber end instead of toward the muzzle. If the chamber, like the bolt assembly, is located in a sealed receiver, combustible gas residues can also flow into the receiver. Although, as a result, a pressure buildup takes place in the receiver, the upper pressure limit remains far below the rupturing pressure of the receiver, even if large numbers of shots are fired, since the receiver is not sealed gas-tight. It has been found, however, that when the gas mixture located in the receiver is ignited, for example, as a result of the ejection of powder particles which are still burning, the pressure in the receiver can increase considerably, which should be avoided. This increase in pressure caused by ignition of the gas mixture contained in the receiver cannot be controlled with an overpressure valve, as the rate of increase of the pressure is very great and the cross-sectional area available for an overpressure valve is relatively small. In addition, an overpressure valve of this type would be a source of malfunctions as a result of a failure to seal, caused, for example, by sand.